Bad virus put to good use: Breakthrough batteries

Enlarge

(PhysOrg.com) -- Viruses have a bad rep--and rightly so. The ability of a virus to quickly and precisely replicate itself makes it a destructive scourge to animals and plants alike. Now an interdisciplinary team of researchers at the University of Maryland's A. James Clark School of Engineering and College of Agriculture and Natural Resources, brought together by Professor Reza Ghodssi, is turning the tables, harnessing and exploiting the"self-renewing"and"self-assembling"properties of viruses for a higher purpose: to build a new generation of small, powerful and highly efficient batteries and fuel cells.

The rigid, rod-shaped Tobacco mosaicvirus(TMV), which under anelectron microscopelooks like uncooked spaghetti, is a well-known and widespread plant virus that devastates tobacco, tomatoes, peppers, and other vegetation. But in the lab, engineers have discovered that they can harness the characteristics of TMV to build tiny components for the lithium ion batteries of the future. They can modify the TMV rods to bind perpendicularly to the metallic surface of a battery electrode and arrange the rods in intricate and orderly patterns on the electrode. Then, they coat the rods with a conductive thin film that acts as a current collector and finally the battery's active material that participates in the electrochemical reactions.

As a result, the researchers can greatly increase the electrode surface area and its capacity to store energy and enable fast charge/discharge times. TMV becomes inert during the manufacturing process; the resulting batteries do not transmit the virus. The new batteries, however, have up to a 10-fold increase in energy capacity over a standard lithium ion battery.

"The resulting batteries are a leap forward in many ways and will be ideal for use not only in small electronic devices but in novel applications that have been limited so far by the size of the required battery,"said Ghodssi, director of the Institute for Systems Research and Herbert Rabin Professor of Electrical and Computer Engineering at the Clark School."The technology that we have developed can be used to produce energy storage devices for integrated microsystems such as wireless sensors networks. These systems have to be really small in size--millimeter or sub-millimeter--so that they can be deployed in large numbers in remote environments for applications like homeland security, agriculture, environmental monitoring and more; to power these devices, equally small batteries are required, without compromising in performance."

You need Flash installed to watch this video

TMV's nanostructure is the ideal size and shape to use as a template for building battery electrodes. Its self-replicating and self-assembling biological properties produce structures that are both intricate and orderly, which increases the power and storage capacity of the batteries that incorporate them. Because TMV can be programmed to bind directly to metal, the resulting components are lighter, stronger and less expensive than conventional parts.

Three distinct steps are involved in producing a TMV-based battery: modifying, propagating and preparing the TMV; processing the TMV to grow nanorods on a metal plate; and incorporating the nanorod-coated plates into finished batteries. It takes an interdisciplinary team of UM scientists and their students to make each step possible.

James Culver, a member of the Institute for Bioscience and Biotechnology and a professor in the Department of Plant Science and Landscape Architecture, and researcher Adam Brown had already developed genetic modifications to the TMV that enable it to be chemically coated with conductive metals. For this project they extract enough of the customized virus from just a few tobacco plants grown in the lab to synthesize hundreds of battery electrodes. The extracted TMV is then ready for the next step.

Scientists produce a forest of vertically aligned virus rods using a process developed by Culver's former Ph.D. student, Elizabeth Royston. A solution of TMV is applied to a metal electrode plate. The genetic modifications program one end of the rod shaped virus to attach to the plate. Next these viral forests are chemically coated with a conductive metal, mainly nickel. Other than its structure, no trace of the virus is present in the finished product, which cannot transmit a virus to either plants or animals. This process is patent-pending.

Ghodssi, materials science Ph.D. student Konstantinos Gerasopoulos, and former postdoctoral associate Matthew McCarthy (now a faculty member at Drexel University) have used this metal-coating technique to fabricate alkaline batteries with common techniques from the semiconductor industry such as photolithography and thin film deposition.

While the first generation of their devices used the nickel-coated viruses for the electrodes, work published earlier this year investigated the feasibility of structuring electrodes with the active material deposited on top of each nickel-coated nanorod, forming a core/shell nanocomposite where every TMV particle contains a conductive metal core and an active material shell. In collaboration with Chunsheng Wang, a professor in the Department of Chemical and Biomolecular Engineering, and his Ph.D. student Xilin Chen, the researchers have developed several techniques to form nanocomposites of silicon and titanium dioxide on the metalized TMV template. This architecture both stabilizes the fragile, active material coating and provides it with a direct connection to the battery electrode.

In the third and final step, Chen and Gerasopoulos assemble these electrodes into the experimental high-capacity lithium-ion batteries. Their capacity can be several times higher than that of bulk materials and in the case of silicon, higher than that of current commercial batteries.

Enlarge

SEM image of Ni/TiO2 nanocomposite electrode (top), cross-section TEM image of an individual nanorod showing the core/shell nanostructure Credit: University of Maryland, College Park

"Virus-enabled nanorod structures are tailor-made for increasing the amount of energy batteries can store. They confer an order of magnitude increase in surface area, stabilize the assembled materials and increase conductivity, resulting in up to a10-fold increase in theenergy capacityover a standardlithium ion battery,"Wang said.

A bonus: since the TMV binds metal directly onto the conductive surface as the structures are formed, no other binding or conducting agents are needed as in the traditional ink-casting technologies that are used for electrode fabrication.

"Our method is unique in that it involves direct fabrication of the electrode onto the current collector; this makes the battery's power higher, and its cycle life longer,"said Wang.

The use of the TMV virus in fabricating batteries can be scaled up to meet industrial production needs."The process is simple, inexpensive, and renewable,"Culver adds."On average, one acre of tobacco can produce approximately 2,100 pounds of leaf tissue, yielding approximately one pound of TMV per pound of infected leaves,"he explains.

At the same time, very tiny microbatteries can be produced using this technology."Our electrode synthesis technique, the high surface area of the TMV and the capability to pattern these materials using processes compatible with microfabrication enable the development of such miniaturized batteries,"Gerasopoulos adds.

While the focus of this research team has long been on energy storage, the structural versatility of the TMV template allows its use in a variety of exciting applications."This combination of bottom-up biological self-assembly and top-down manufacturing is not limited to battery development only,"Ghodssi said."One of our lab's ongoing projects is aiming at the development of explosive detection sensors using versions of the TMV that bind TNT selectively, increasing the sensitivity of the sensor. In parallel, we are collaborating with our colleagues at Drexel and MIT to construct surfaces that resemble the structure of plant leaves. These biomimetic structures can be used for basic scientific studies as well as the development of novel water-repellent surfaces and micro/nano scale heat pipes."

Source

Pure nanotube-type growth edges toward the possible

New research at Rice University could ultimately show scientists the way to make batches of nanotubes of a single type.

A paper in the online journalPhysical Review Lettersunveils an elegant formula by Rice University physicist Boris Yakobson and his colleagues that defines the energy of a piece of graphene cut at any angle.

Yakobson, a professor in mechanical engineering and materials science and of chemistry, said this alone is significant because the way graphene handles energy depends upon the angle -- or chirality -- of its edge, and solving that process for odd angles has been extremely challenging. But, he wrote, the research has"profound implications in the context of nanotube growth, offering rational ways to control their chiral symmetry, a tantalizing yet so far elusive goal."

Graphene is the single-atom-thick form of carbon that has become of tremendous interest for its potential to revolutionize electronics, optics, sensing and mechanical devices. Getting a handle on how this chicken-wire-shaped sheet of carbon atoms transports electricity has been the focus of intense study.

A sheet of graphene with zigzag or armchair edges squares up nicely. Zigzags are metallic, armchairs are semiconductors, and their atoms march in rank, evenly spaced, along the edges. A full 30 degrees of rotation separates one from the other.

But if the hexagons that make up a sheet are offset less than 30 degrees, atoms along a straight edge are unevenly spaced."That makes analysis of the energy very complicated, because it's a large irregular structure. It's like noise,"Yakobson said."We've found a way to calculate the energies in these arbitrary angles,"he said.

Yakobson and his co-authors, Yuanyue Liu, a graduate student in his lab, and Alex Dobrinsky, a former graduate student and now a postdoctoral researcher at Brown University, soon wondered how these findings applied to carbon nanotubes.

"There are as many ways to roll graphene into a nanotube as there are ways to roll a newspaper,"Yakobson said."The text can be aligned circumferentially or run straight along the axis or spiral at an angle."

While rolling a newspaper makes it hard to read, rolling carbon into a nanotube makes it relatively easy to"read"its type -- whether armchair or zigzag or some variation in between. What's impossible is controlling how the tube will roll. The process tends to be willy-nilly, leaving researchers the task of separating the nanotubes they need from the bulk through ultracentrifugation or other expensive procedures.

Yakobson said it would be a real game-changer if they could, for instance, grow batches of pure armchair nanotubes for use in such projects as armchair quantum nanowire (AQW). As imagined by Rice's late Nobel Laureate Richard Smalley, AQW could revolutionize the nation's power grid by carrying 10 times the amount of electricity as copper at only one-sixth the weight.

Yakobson's work may open a path to do so. A nanotube's chirality is determined by the combination of energies at play in its nucleation."When it just emerges from the 'primordial soup' of carbon, the edge of the tube is essentially the same as the edge of graphene,"he said.

"At first, it's just a cap. There's no stem yet. You're frying these caps on a skillet, and they're bubbling,"he said."The probability for different bubbles to emerge is controlled by energy around the edge."

The chirality of the nascent nanotube is set when atoms in the cap self-assemble a sixth pentagon (necessary to mold the hexagons into a dome)."That's where we can, I think for the first time, make some quantitative judgment about how different chiral structures emerge,"Yakobson said.

It may be worth chemists' efforts to look more closely at the energy between the catalyst and carbon structure."This has some promise,"he said."If you can tweak this preference, if you can change energy from the catalyst side, you change the preference of the chirality. And then you can tell these self-assembling carbons, 'Please dance this way; don't dance that way.'"

Yakobson hopes the new work helps solve the long-standing problem of nanotube chirality."For almost two decades, we didn't have a good understanding of this process,"he said."Actually, we didn't have a clue. I'm not saying this is a full solution, but this is the first time we've seen a quantitative approach, an order in the seeming chaos. It just feels satisfying.

"The bottom line is simple. We figured out the graphene edge and bridged it to the holy grail ofnanotubes, which is chirality control."

Source

Triple-mode transistors show potential: Researchers introduce graphene-based amplifiers

Enlarge

(PhysOrg.com) -- Rice University research that capitalizes on the wide-ranging capabilities of graphene could lead to circuit applications that are far more compact and versatile than what is now feasible with silicon-based technologies.

Triple-mode, single-transistor amplifiers based ongraphene-- the one-atom-thick form of carbon that recently won its discoverers aNobel Prize-- could become key components in futureelectronic circuits. The discovery by Rice researchers was reported this week in the online journalACS Nano.

Graphene is very strong, nearly transparent and conducts electricity very well. But another key property is ambipolarity, graphene's ability to switch between using positive and negative carriers on the fly depending on the input signal. Traditionalsilicon transistorsusually use one or the other type of carrier, which is determined during fabrication.

A three-terminal single-transistoramplifiermade of graphene can be changed during operation to any of three modes at any time using carriers that are positive, negative or both, providing opportunities that are not possible with traditional single-transistor architectures, said Kartik Mohanram, an assistant professor of electrical and computer engineering at Rice. He collaborated on the research with Alexander Balandin, a professor of electrical engineering at the University of California, Riverside, and their students Xuebei Yang (at Rice) and Guanxiong Liu (at Riverside).

Mohanram likened the new transistor's abilities to that of a water tap."Turn it on and the water flows,"he said."Turn it off and the water stops. That's what a traditional transistor does. It's a unipolar device -- it only opens and closes in one direction."

"But if you close a tap too much, it opens again and water flows. That's what ambipolarity is -- current can flow when you open the transistor in either direction about a point of minimum conduction."

That alone means a graphene transistor can be"n-type"(negative) or"p-type"(positive), depending on whether the carrier originates from the source or drain terminals (which are effectively interchangeable). A third function appears when the input from each carrier is equal: The transistor becomes a frequency multiplier. By combining the three modes, the Rice-Riverside team demonstrated such common signaling schemes as phase and frequency shift keying for wireless and audio applications.

"Our work, and that of others, that focuses on the applications of ambipolarity complements efforts to make a better transistor with graphene,"Mohanram said."It promises more functionality."The research demonstrated that a single graphene transistor could potentially replace many in a typical integrated circuit, he said. Graphene's superior material properties and relative compatibility with silicon-based manufacturing should allow for integration of such circuits in the future, he added.

Technological roadblocks need to be overcome, Mohanram said. Such fabrication steps as dielectric deposition and making contacts"wind up disturbing the lattice, scratching it and introducing defects. That immediately degrades its performance (limiting signal gain), so we have to exercise a lot of care in fabrication.

"But the technology will mature, since so many research groups are working hard to address these challenges,"he said.

Source

Microbial hair -- it's electric: Specialized bacterial filaments shown to conduct electricity

Enlarge

(PhysOrg.com) -- Some bacteria grow electrical hair that lets them link up in big biological circuits, according to a University of Southern California biophysicist and his collaborators.

The finding suggests that microbial colonies may survive, communicate and share energy in part through electrically conducting hairs known as bacterial nanowires.

"This is the first measurement of electron transport along biological nanowires produced by bacteria,"said Mohamed El-Naggar, assistant professor of physics and astronomy at the USC College of Letters, Arts and Sciences.

El-Naggar was the lead author of a study appearing online next week inProceedings of the National Academy of Sciences.

Knowing howmicrobial communitiesthrive is the first step in finding ways to destroy harmful colonies, such as biofilms on teeth. Biofilms have proven highly resistant toantibiotics.

The same knowledge could help to promote useful colonies, such as those in bacterial fuel cells under development at USC and other institutions.

"The flow of electrons in various directions is intimately tied to the metabolic status of different parts of thebiofilm,"El-Naggar said."Bacterial nanowires can provide the necessary links… for the survival of a microbial circuit."

A bacterial nanowire looks like a long hair sticking out of a microbe's body. Like human hair, it consists mostly of protein.

To test the conductivity of nanowires, the researchers grew cultures of Shewanella oneidensis MR-1, a microbe previously discovered by co-author Kenneth Nealson, Wrigley Professor of Geobiology at USC College.

Shewanella tend to make nanowires in times of scarcity. By manipulating growing conditions, the researchers produced bacteria with plentiful nanowires.

The bacteria then were deposited on a surface dotted with microscopic electrodes. When a nanowire fell across two electrodes, it closed the circuit, enabling a flow of measurable current. The conductivity was similar to that of a semiconductor– modest but significant.

When the researchers cut the nanowire, the flow of current stopped.

Previous studies showed that electrons could move across a nanowire, which did not prove that nanowires conducted electrons along their length.

El-Naggar's group is the first to carry out this technically difficult but more telling experiment.

Electricity carried on nanowires may be a lifeline. Bacteria respire by losing electrons to an acceptor– for Shewanella, a metal such as iron. (Breathing is a special case: Humans respire by giving up electrons to oxygen, one of the most powerful electron acceptors.)

Nealson said of Shewanella:"If you don't give it an electron acceptor, it dies. It dies pretty rapidly."

In some cases, a nanowire may be a microbe's only means of dumping electrons.

When an electron acceptor is scarce nearby, nanowires may help bacteria to support each other and extend their collective reach to distant sources.

The researchers noted that Shewanella attach to electron acceptors as well as to each other, forming a colony in which every member should be able to respire through a chain of nanowires.

"This would be basically a community response to transfer electrons,"El-Naggar explained."It would be a form of cooperative breathing."

El-Naggar and his team are among the pioneers in a young discipline. The term"bacterial nanowire"was coined in 2006. Fewer than 10 studies on the subject have been published, according to co-author Yuri Gorby of The J. Craig Venter Institute in San Diego, discoverer of nanowires in Shewanella.

Gorby and others became interested in nanowires when they noticed that reduction of metals appeared to be occurring around the filaments. Since reduction requires the transfer of electrons to a metal, the researchers suspected that the filaments were carrying a current.

Nanowires also have been proposed as conductive pathways in several diverse microbes.

"The current hypothesis is that bacterial nanowires are in fact widespread in the microbial world,"El-Naggar said.

Some have suggested that nanowires may help bacteria to communicate as well as to respire.

Bacterial colonies are known to share information through the slow diffusion of signaling molecules. Nealson argued thatelectron transportovernanowireswould be faster and preferable for bacteria.

"You want the telegraph, you don't want smoke signals,"he said.

Bacteria's communal strategy for survival may hold lessons for higher life forms.

In an op-ed published in Wired in 2009, Gorby wrote:"Understanding the strategies for efficient energy distribution and communication in the oldest organisms on the planet may serve as useful analogies of sustainability within our own species."

Source

Scientists create world's first 'super-twisted' light

(PhysOrg.com) -- The research team at the University of Glasgow twisted the light like a corkscrew by using a polarising filter, before shining it onto a specially shaped piece of gold to create the world's first 'super twisting'.

Super twisted light does not exist in nature and, until now, it had only been theorised by scientists, never produced.

Super twisted light can be used to findproteintraces in incredibly small samples ofbiological materiallike blood, far less than currently used.

The researchers have already used the light to look at many different proteins and have found that it is particularly sensitive to the structures of proteins which cause degenerative diseases such as Alzheimer’s and Parkinson’s Disease.

The findings have been published inNature Nanotechnology.

Dr Malcolm Kadodwala, senior lecturer in the School of Chemistry, said:“We are very excited by this research. Essentially, this twisted light, which does not exist naturally, allows us to detect biological materials at unprecedented low concentrations.

“Due to the nature of the twisted light, it has been shown to be particularly effective at detecting proteins with a structure characteristic of amyloids– insoluble proteins that can stick together to form plaques within different organs in the body.

“It is these plaques which are thought to play a part in neurodegenerative diseases such as Alzheimer’s, Parkinson’s and CJD– though the reasons for this are unclear.

“We’re now looking to see if this same technique can be adapted to detect a wider range of proteins which are indicative of other diseases. The fact this method requires much less material (just one picogram or million millionth of a gram) for analysis than current techniques and uses a form of light previously unrealised is a big step forward.”

The complex science behind the technique takes advantage of the fact light can be twisted like a corkscrew by passing it through a special polarising filter: in much the same way as polarised sunglasses allow only certain alignments of light waves through.

By shining light onto a specially-shaped piece of metal– in this case gold– the light that is emitted from the metal becomes super-twisted.

Polarised or twisted light is already used in some medical techniques to analyse biomolecules, however the multidisciplinary Glasgow team, have been able to achieve a much more powerful system by twisting the light even tighter.

The team included engineer Dr Nikolaj Gadegaard and life scientist, Dr Sharon Kelly, with a team of physicists at the University of Exeter, led by Dr Euan Hendry.

The use of super-twisted light in spectroscopy– the analysis of materials according to way they absorb and emit light– has numerous potential applications in biosensing and could also be used to detect particular types of viruses which have similar structures.

Source

Physicists use graphene to decode DNA

Enlarge

Genome sequencing will have a profound effect on our understanding of genetic biology and could usher in a day when doctor and patient are able to review individual genome sequences to fully personalise medical treatment.

As theX PRIZE FOUNDATIONbegins to receive nominations for its $10m prize for the first privately funded company that can accurately sequence 100 genomes in 10 days for less than $10,000 per genome, the science writer Philip Ball looks at the latest advances towards success in DecemberPhysics World's lead feature.

The baton, once firmly in the hands of chemists and biologists, has been grabbed by physicists around the world since the mid-1990s when David Deamer from the University of California, Santa Cruz imagined threading aDNA strandthrough a tiny pore -- reading out the chemical bases strung along the strand as it passes through. His idea was that in a salt solution, the number of dissolved ions passing through the pore would vary depending on which base was sitting in the pore.

Over the past decade, scientists have sought means to use Deamer's technique with far greater control of the pore and the movement of DNA through the pore, while also contemplating how the technique can be turned into a handy device that could be used in doctors' surgeries worldwide.

Initial thoughts were towards the use of a silicon-nitride nanopore but researchers have found the material a little too thick, meaning that more than one nucleotide -- the structural units that make up DNA -- can be in the pore at any one time.

Now, however, graphene -- one-atom thick sheets of carbon that led to this year's Nobel Prize for Physics -- is generating huge excitement as a possible DNA sequencing material following the work of three independent research groups earlier this year.

The teams -- based at the universities of Delft, Pennsylvania and Harvard -- have each drawn DNA through a nanopore drilled into graphene. As the materials is so much thinner thansilicon nitride, the teams are reported to believe that graphene may be a"game changer".

Whether for the physicists it's the lure of a $10m prize, the joy of basic research, or the satisfaction of designing a technique that could revolutionize medicine, it looks like graphene -- already dubbed a"wonder material on account it being ultrathin, ultrastrong and a great electrical conductor -- could be adding one more string to its already powerful bow.

Source